1. Field of the Invention
The present invention pertains to a surgical prosthesis, and, more particularly, pertains to a synthetic vascular graft implantable prosthesis.
2. Description of the Prior Art
Diseases affecting the cardiovascular system are either congenital or acquired. An acquired cardiovascular disease can result from living habits, infections or injuries during embryonic life, or at any time following birth. Some diseases primarily affect the blood vessels; others only the heart itself.
Atherosclerosis is the major disease that affects the blood vessels. This disease may have its beginnings early in life and is first noted as a thickening of the arterial walls. This thickening is an accumulation of fat, fibrin, cellular debris and calcium. The resultant narrowing of the internal lumen of the vessel is called stenosis. Vessel stenosis impedes and reduces blood flow. Hypertension and dysfunction of the organ or area of the body that suffered the impaired blood flow can result.
As the buildup on the inner wall of a vessel thickens, the vessel wall loses the ability to expand and contract. Also, the vessel loses its viability and becomes weakened and susceptible to bulging, also known as aneurysm. In the presence of hypertension or elevated blood pressure, aneurysms will frequently dissect and ultimately rupture.
Small vessels, such as the arteries that supply blood to the heart, legs, intestines and other areas of the body, are particularly susceptible to atherosclerotic narrowing. The loss of blood supply to the leg or segment of the intestine may result in gangrene. Atherosclerotic narrowing of the coronary arteries impedes, limits and in some instances prevents blood flow to regional areas of the heart. Depending upon its severity and location within the coronary circulation, pain, cardiac dysfunction or death may result.
Vascular complications produced by a atherosclerosis, such as, stenosis, aneurysm, rupture and occlusion are, in the majority of cases, managed either medically or surgically. Control and elimination of hypertension is the more effective form of medical management. In cases in which atherosclerotic disease is advanced and the attendant complications jeopardize the health of the patient, surgical intervention is usually instituted.
Aneurysms and stenosis of major arteries are best corrected by a plastic reconstruction that does not require any synthetic graft or patch materials. However, if the disease is extensive and the vessel is no longer reliable, it is usually replaced by a graft. In such case, the involved vessel section is transected and removed and a synthetic patch, conduit or graft is sewn into place.
Medium sized arteries are operated on much the same as for large diameter vessels. But in some types of surgery where the replacement graft is of small diameter, handling and surgical placement of the graft is difficult. The internal diameter may be compromised due either to surgical technique or biological response. In some cases, the graft may become entirely occluded shortly after surgery.
Patients with coronary artery disease in which blood flow to part of the heart muscle has been compromised receive significant benefit from coronary artery bypass surgery. This type of surgery requires the use of grafts of small diameter. These grafts, the majority of which are biologic, have certain inherent problems. Synthetic grafts are only used on infrequent occasions because they are more problematical than biologic grafts. It is the purpose of this invention to obviate and eliminate certain of the more significant problems associated with the surgical procedure of coronary artery bypass and the implanted grafts following surgery.
In a patient who undergoes coronary artery bypass surgery, a non-critical artery or vein of small diameter is harvested from elsewhere in the body and sewn into place in a manner that reestablishes flow to the area of the heart that earlier lost its blood supply because of atherosclerotic blockage and is referred to as an autograft. When no suitable artery or vein can be harvested, an allograft or xenograft vessel may be employed. However, experience with these latter two graft types is limited because of unsatisfactory results. A synthetic graft is an alternative to an allograft or a xenograft. But, like the allograft and xenograft, the synthetic counterpart does not produce acceptable results.
Although the heart benefits immediately from the reestablished blood supply of the bypass, there is no assurance the graft will function trouble free indefinitely. The autograft, because it is harvested from the patient, who in all probability is being operated on for atherosclerotic artery disease, is highly susceptible to atherosclerosis following surgery. Most harvested veins used in coronary artery bypass surgery exhibit some degree of atherosclerosis.
The long vein in the leg called the saphenous vein is the most commonly harvested vein for use as a vein bypass graft, (autograft), in coronary artery surgery. Most saphenous vein bypass grafts, in time, exhibit a narrowing of the lumen unlike that of atherosclerosis. It is believed this is a pathologic response of the vein because it is of different cellular construction and composition than an artery--a condition for which it is not best suited. Harvesting a saphenous vein autograft is a tedious surgical task and not always rewarded with the best quality graft. Also, removal of the saphenous vein disrupts the natural venous blood return from the leg and is not therapeutically recommended except for medical reasons such as in a patient with advanced venous disease such as varicose veins. Finally, harvesting an autograft in the operating rooms requires additional surgical time and expense.
These noted limitations of the saphenous vein autograft have generated interest in a synthetic graft for coronary artery bypass. Clinical experience with small diameter synthetic grafts for coronary artery bypass dates back to the mid 1970's. Teflon and Dacron fibers are the most commonly employed materials for synthetic grafts. However, despite the different methods and techniques of graft construction such as woven or knit, velour, texturized or non-texturized, tight or loose, fine or coarse, expanded or non-expanded, variations in fiber diameter and wall thickness, etc., no graft of small lumen diameter has shown a resistance to blockage by thrombus. However, synthetic grafts of large diameter consistently remain patent and trouble-free for extended periods of many years. This finding is consistently repeated where a small-diameter synthetic graft is used to bypass a blocked coronary artery. Therefore, despite their inherent limitations, autografts employing the saphenous vein remain the graft of choice for coronary artery bypass surgery.
The coronary artery circulation begins with the right and left coronary arteries. These two arteries in turn give rise to an extensive coronary circulation. Generally, atherosclerosis affects the larger coronary arteries. Therefore, a patient being operated upon for coronary artery disease will receive two or more vein grafts of various length and diameter depending upon the location of the blockage and the usable harvested saphenous vein.
Even though coronary artery bypass surgery is widely practiced and has become a routine procedure in hospitals throughout the world, it is not without certain operative limitations that would best be avoided. Sewing the graft to the host vessel, known as an anastomosis, requires delicate surgical techniques to accomplish the best possible result. There are several complications to be avoided when anastomosing a vessel and graft together. It is important that the junction between the host tissue and graft be a uniform transition without narrowing and regional irregularities such as protuberances that bulge into the lumen or sinuses that extend outward of the lumen. A narrowing at the site of anastomosis reduces blood flow. Protuberances into the lumen obstruct blood flow and may produce turbulence. Lastly, blood that stagnates in a sinus or cavity tends to clot and obstruct the vessel lumen and subsequently the blood flow. All these characteristics diminish the effectiveness and patency of the graft.
Summarizing, the limitations associated with the autograft as applied in coronary artery bypass surgery are: tedious surgical task to harvest, physically imperfect and irregular lumen, tedious surgical task to anastomose to host vessel, physically imperfect anastomosis of irregular and unsmooth transition between graft and vessel, functional narrowing of vein graft lumen during early postoperative period, and occlusion of the autograft due to thrombosis and/or continuance of the preexisting atherosclerotic process.
The synthetic vascular graft of the present invention overcomes the deficiencies of the prior art and provides a synthetic vascular graft that significantly improves the results of coronary artery bypass surgery. This synthetic vascular graft eliminates the time of the tedious surgical task of harvesting a saphenous vein. The lumen of the synthetic vascular graft is not comprised of natural anatomical irregularities as those that are common to the prior art vein grafts. The synthetic vascular graft minimizes the task of forming anastomotic connections to the ascending aorta at the proximal end and the coronary artery distally. The synthetic vascular graft also does not exhibit narrowing associated with implants of the saphenous vein grafts and will not exhibit occlusion and blockage due to atherosclerosis.